Nozzle for injection moulding of plastic materials

ABSTRACT

Nozzle ( 1 ) for injection moulding of plastic materials, comprising a generally cylindrical body ( 2 ) with spiral-shaped groove ( 4 ) on the external surface, in which a first and a second heating resistor ( 5, 6 ), which are independent from each other and which are equipped with respective autonomous controlling thermocouples ( 7, 8 ), are wound.

FIELD OF THE INVENTION

[0001] This invention relates in general to injection moulding forplastic materials and, more specifically, to a nozzle for said injectionmoulding, of the type comprising a generally cylindrical body with aheating resistor wound on the external surface which is operativelyconnected to a controlling thermocouple.

[0002] In nozzles of this kind, the function of the heating resistor isevidently to keep the temperature of the nozzle at predefined valuesaccording to the composition of the melt plastic material to beinjected. The thermocouple is connected to an automatic moulding processelectronic control unit, which controls the electrical power to theheating resistor.

[0003] In such nozzles currently in use, an example of which isdescribed and illustrated in European Patent EP-B-0750975 by MOLDMASTERS LIMITED, the efficiency of the moulding process automaticcontrol is closely connected to the functionality, i.e. reliability, ofthe heating resistor and the respective thermocouple. This is because,in the event of failures to either one of the two components, thetemperature of the injected plastic material can no longer be controlledin a suitable fashion, with consequent degrading of the mouldingprocess. On the other hand, replacing the heating resistor or theassociated thermocouple would mean stopping the moulding apparatus andbe a critical problem, considering the high number of nozzles commonlyused in one moulding apparatus.

SUMMARY OF THE INVENTION

[0004] The object of this invention is to overcome said problem.According to this invention, this object is attained by a nozzle whichis provided with a second heating resistor, wound on the externalsurface, independent from said first heating resistor, and provided withan autonomous control thermocouple.

[0005] Thanks to this idea, the nozzle, and consequently the mouldingapparatus where the nozzle is fitted, ensures confidence of operationwhich is double with respect to that of a traditional nozzle. Thethermocouples of the two heating resistors are connected to the mouldingprocess electronic control unit so as to selectively activate either oneor the other of the two resistors according to their effectivefunctionality. The two thermocouples can also be calibrated todifferentiated values.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The invention will be better explained by the following detaileddescription with reference to the accompanying drawings purely providedas non-limiting example, in which:

[0007]FIG. 1 schematically illustrates a simplified form of an axialcross-section of the nozzle for plastic material injection mouldingaccording to a first embodiment of the invention, and

[0008]FIG. 2 shows a variant of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0009] With reference to FIG. 1, numeral 1 generally refers to a nozzlefor plastic material injection moulding according to this invention. Itmust be stressed that, for the sake of simplicity of the illustration,the drawing only shows the external body of the nozzle, while the valveconsisting of a mobile pin axially reciprocating and co-operating with acorresponding annular valve seat is omitted.

[0010] The body of the nozzle 1, generally indicated by numeral 2, isgenerically cylindrical with an internal axial passage 3. Aspiral-shaped groove 4 is made in the external side of the body 2, inwhich a first heating resistor 5 and, according to this invention, asecond heating resistor 6 are wound.

[0011] The resistors 5 and 6 are entirely independent from each other ona functional point of view.

[0012] In the shown embodiment the resistors 5 and 6 are arranged in aradially superimposed condition in the spiral-shaped groove 4, which hasa depth correspondigly adapted to house both therein.

[0013] The two resistors 5, 6 are electrically connected independentlyone with respect to the other to a source of electrical power, viarespective connection terminals which are not visible in the drawing andwhich are operatively connected (in a way which is known and howeverwithin the grasp of sector technicians) each with a respectivethermocouple 7, 8.

[0014] The two thermocouples 7, 8, arranged in correspondence with theend of the body 2 destined to face inside the injection mould, are inturn independently connected to a moulding process electronic controlunit (conventional and not shown in the drawings), which controls theelectrical power to either one or the other resistor 5, 6 according tothe predefined moulding process parameters. The electronic control unitalso selects either one of the two resistors 5, 6 according to theireffective functionality. In this way, for example, the first heatingresistor 5 will be normally operative, while the second resistor 6 willbe kept as a backup, to be made operative in the case of a failureconcerning the first resistor 5 or the respective thermocouple 7.

[0015] A differentiated operation of the two resistors 5, 6, which arealso automatically managed by part of the electronic control unit willbe possible, if required by operating on the calibration of therespective thermocouples 7, 8. The variant shown in FIG. 2 is generallysimilar to the embodiment disclosed with reference to FIG. 1, and onlythe difference shall be disclosed in detail. In this variant theresistors 5 and 6 are arranged in an axially side-by-side condition inthe spiral-shaped groove 4, which in this case has a widthcorrespondigly adapted to house both therein.

[0016] Naturally, numerous changes can be implemented to theconstruction and forms of embodiment of the invention herein envisaged,all comprised within the context of the concept characterising thisinvention, as defined by the following claims.

What is claimed is:
 1. Nozzle (1) for injection moulding of plasticmaterials comprising a generally cylindrical body (2) having an externalsurface and a heating resistor (5) wound on said external surface and towhich a controlling thermocouple (7) is operatively connected, and alsocomprising a second heating resistor (6) wound on said external surfaceof the body (2), independent from said heating resistor (5) and equippedwith an autonomous second controlling thermocouple (8).
 2. Nozzleaccording to claim 1, in which said heating resistor (5) is housed in aspiral-shaped groove (4) of said cylindrical body (2), wherein saidsecond heating resistor (6) is also housed in said spiral-shaped groove(4) in a superimposed condition with said heating resistor (5). 3.Nozzle according to claim 1, in which said heating resistor (5) ishoused in a spiral-shaped groove (4) of said cylindrical body (2),wherein said second heating resistor (6) is also housed in saidspiral-shaped groove (4) in a side-by-side condition with said heatingresistor (5).